MEMS accelerometer with proof masses moving in an anti-phase direction

ABSTRACT

A sensor is disclosed. The sensor includes a substrate and a mechanical structure. The mechanical structure includes at least two proof masses including a first proof mass and a second proof mass. The mechanical structure also includes a flexible coupling between the at least two proof masses and the substrate. The at least two proof masses move in an anti-phase direction normal to the plane of the substrate in response to acceleration of the sensor normal to the plane and move in anti-phase in a direction parallel to the plane of the substrate in response to an acceleration of the sensor parallel to the plane. The at least two proof masses move in a direction parallel to the plane of the substrate in response to an acceleration of the sensor parallel to the plane.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent application Ser. No. 14/188,173, filed Feb. 24, 2014, entitled “MEMS ACCELEROMETER WITH PROOF MASSES MOVING IN ANTI-PHASE DIRECTION NORMAL TO THE PLANE OF THE SUBSTRATE,” which claims benefit under 35 USC 119(e) of U.S. Provisional Patent Application No. 61/920,246, filed on Dec. 23, 2013, entitled “MEMS ACCELEROMETER WITH PROOF MASSES MOVING IN ANTI-PHASE DIRECTION NORMAL TO THE PLANE OF THE SUBSTRATE,” all of which are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates generally to inertial sensors and more particularly to MEMS accelerometers.

BACKGROUND

Inertial sensors such as accelerometers are widely used for motion sensing applications. Conventionally, an accelerometer consists of a suspended proof mass and a means of measuring the proof mass displacement with respect to the reference frame. There is always a need to provide improvements in the performance and reliability of an accelerometer for commercial applications. Typically, performance is determined by the mechanical and electrical sensitivities of the sensor and reliability is determined, among many other parameters, by the required breakout force to unstuck moving parts of the structure in case of accidental contact with other fixed or moving parts.

What is needed therefore is a system and method that provides such inertial sensors. The method and system should be easily implemented, cost effective and adaptable to existing environments. The present invention addresses the above-identified issues.

SUMMARY

A sensor is disclosed. In a first aspect, the sensor includes a substrate and a mechanical structure. The mechanical structure includes at least two proof masses including a first proof mass and a second proof mass. The mechanical structure includes a flexible coupling between the at least two proof masses and the substrate. The at least two proof masses move in an anti-phase direction normal to a plane of the substrate in response to acceleration of the sensor via an unbalancing torque and move in anti-phase in a direction parallel to the plane of the substrate in response to an acceleration of the sensor in the same direction via an unbalancing torque.

In a second aspect, the sensor includes a substrate and a mechanical structure. The mechanical structure includes at least two proof masses including a first proof mass and a second proof mass. The mechanical structure includes a flexible coupling between the at least two proof masses and the substrate. The at least two proof masses move in an anti-phase direction normal to a plane of the substrate in response to acceleration of the sensor via an unbalancing torque and move in a direction parallel (Y) to the plane of the substrate in response to an acceleration of the sensor in the same direction.

In a third aspect, the sensor includes a substrate and a mechanical structure. The mechanical structure includes at least two proof masses including a first proof mass and a second proof mass. The mechanical structure includes a flexible coupling between the at least two proof masses and the substrate. The at least two proof masses move in an anti-phase direction normal to a plane of the substrate in response to acceleration of the sensor via an unbalancing torque move in anti-phase in a first direction parallel (X) to the plane of the substrate in response to an acceleration of the sensor in the same direction via an unbalancing torque and move in a second direction parallel (Y) to the plane of the substrate in response to an acceleration of the sensor in the same direction.

In a fourth aspect, the sensor includes a substrate and a mechanical structure. The mechanical structure includes at least two proof masses including a first proof mass and a second proof mass. The mechanical structure includes a flexible coupling between the at least two proof masses and the substrate. The at least two proof masses move in anti-phase in a direction parallel (X) to the plane of the substrate in response to an acceleration in the same direction of the sensor via an unbalancing torque.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an accelerometer that responds to a linear acceleration in a Z direction.

FIG. 2 shows a single anchor accelerometer in accordance with an embodiment.

FIG. 3 shows a single lever and single anchor accelerometer in accordance with an embodiment.

FIG. 4 shows an alternative single lever accelerometer in accordance with an embodiment.

FIG. 5a shows the configuration of the sensor to be a capacitive wheatstone bridge in accordance with an embodiment.

FIG. 5b shows a configuration for sensing acceleration in a Wheatstone bridge configuration as shown in accordance with an embodiment.

FIG. 5c shows a configuration for sensing magnetic field in a Wheatstone bridge configuration as shown in accordance with an embodiment.

FIG. 6 shows an accelerometer where a capacitive readout is performed on a rotational lever instead on proof masses in accordance with an embodiment.

FIG. 7 shows an accelerometer including the tilt cancellation paddles in accordance with an embodiment.

FIG. 8 shows a combined accelerometer and magnetometer sensor in accordance with an embodiment.

FIGS. 9-12 show a various embodiments of sensors that includes a cap as part thereof.

FIGS. 13a-13c illustrate another embodiment of an accelerometer 1000 in accordance with the present invention

DETAILED DESCRIPTION

The present invention relates generally to inertial sensors and more particularly to MEMS accelerometers. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodiments and the generic principles and features described herein will be readily apparent to those skilled in the art. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features described herein.

In the described embodiments micro-electro-mechanical systems (MEMS) refers to a class of structures or devices fabricated using semiconductor-like processes and exhibiting mechanical characteristics such as the ability to move or deform. MEMS devices often, but not always, interact with electrical signals. MEMS devices include but are not limited to gyroscopes, accelerometers, magnetometers, pressure sensors, microphones, and radio-frequency components. Silicon wafers containing MEMS structures are referred to as MEMS wafers.

In the described embodiments, the MEMS device may refer to a semiconductor device implemented as a micro-electro-mechanical system. The MEMS structure may refer to any feature that may be part of a larger MEMS device. The semiconductor layer with the mechanically active MEMS structure is referred to as the device layer. An engineered silicon-on-insulator (ESOI) wafer may refer to a SOI wafer with cavities beneath the silicon device layer or substrate. A handle wafer typically refers to a thicker substrate used as a carrier for the thinner silicon device substrate in a silicon-on-insulator wafer. A handle substrate and a handle wafer can be interchanged.

In the described embodiments, a cavity may refer to an opening or recession in a substrate wafer and an enclosure may refer to a fully enclosed space. A post may be a vertical structure in the cavity of the MEMS device for mechanical support. A standoff is a vertical structure providing electrical contact.

In the described embodiments, a rigid structure within a MEMS device that moves when subject to force may be referred to as a plate. Although rigid plates are preferred for the described embodiments, semi rigid plates or deformable membranes could replace rigid plates. Plates may comprise of silicon, silicon containing materials (e.g. poly-silicon, silicon oxide, silicon nitride), metals and materials that are used in semiconductor processes (e.g. aluminum nitride, germanium). A back plate may be a solid or perforated plate comprising at least one electrode. The electrode can be comprised of semiconductor process compatible conductive materials (e.g. poly-silicon, silicon, aluminum, copper, nickel, titanium, chromium, gold). The electrodes may have insulating films on one or more surfaces.

FIG. 1 shows top and side views of an accelerometer 100 that responds to a linear acceleration in a Z direction. The accelerometer 100 comprises two proof masses PM1 102B and PM2 102A that respond to a linear acceleration in the Z direction by moving in anti-phase direction normal to a plane of a substrate 106. The anti-phase movement is constrained by a flexible coupling between the two proof masses PM1 102B and PM2 102A and the substrate 106. The flexible coupling comprises two separated anchors A1 110A and A2 110B, two central torsional springs B1 114A and B2 114B, two rotational levers L1 116A and L2 116B and four external torsional springs B11 118A, B21 118B, B12 118C and B22 118D. The motion of the accelerometer 100 is measured by an out-of-plane transducer on the proof masses, for instance a set of capacitive differential electrode C1 and C2 120A-120D.

The springs B1 114A and B2 114B connect the anchors A1 110A and A2 110B to the levers L1 116A and L2 116B. The four external torsional springs B11 118A, B21 118B, B12 118C and B22 118D connect the end of one lever to the end of the other lever on the opposite side trough the two proof masses PM1 102B and PM2 102A. In particular spring B11 118A connects the top of the left lever L1 116A to internal proof mass PM1 102B that connects the bottom of the right lever L2 116B trough the spring B22 118D. In the same way the bottom of the left lever L1 116A is coupled to the top of the right lever L2 116B with the springs B12 118C and B22 118D.

For simplicity, suppose that the proof masses have the center of gravity on the axis of the central springs (B1 114A and B2 114B) and that the external springs (B12 118C, B21 118B, B11 118A and B22 118D) are coupled to the proof masses with the same distance from the center of gravity orthogonal to this axis. A more general case is described in the following.

A linear acceleration a in the Z direction will create a force in Z for each proof mass: F_(PM) ₁ =m₁a P_(PM) ₂ =m₂a Where m₁ and m₂ are the masses of PM1 102B and PM2 102A respectively. On each proof mass half of this force acts on each one of the external springs, B11 118A and B22 118D for PM1 102B and B12 118C and B21 118B for PM2 102A. Finally this force is transferred on the extreme of the lever so in the center of the lever there is a torque that is the difference of this force times the lever of PM1 102B and PM2 102A:

$M = {{\frac{m_{1}a}{2}l_{{PM}\; 1}} - {\frac{m_{2}a}{2}l_{{PM}\; 2}}}$ where the lever length of PM1 l_(PM1) is the distance from the springs B11 118A to B1 114A and B22 118D to B2 114B and l_(PM2) is the distance from the springs B12 118C to B1 114A and B21 118B to B2 114B. The torque M causes the central springs and the two levers to rotate in anti-phase and so one proof mass moves towards the substrate and the other moves in the opposite direction.

In order to cause the anti-phase movement there must be an unbalancing torque M. This unbalanced torque M can be given by a difference in the mass (m₁≠m₂), by difference in the lever (l_(PM1)≠l_(PM2)), or by a difference in the mass lever product (m₁l_(PM1)≠m₂l_(PM2)).

In a more general example, where the center of gravity of the mass is not lying on the spring axis or the external springs are not coupled to proof masses with the same distance orthogonal to this axis, the acceleration cause a torque in addition to the force in the Z direction. In this case the structure of sensor also rotates. The sensor also includes a transducer to measure the motion of the sensor. For instance capacitive sensing can be performed by means of electrodes on the substrate measuring the capacitance change due to the mass motion.

Single Anchor Accelerometer

FIG. 2 shows a single anchor accelerometer 200 in accordance with an embodiment. The single anchor comprises an anchor A 210B, two central springs B1 214A and B2 214B, torsional springs B11 218A, B21 218B, B12 218C and B22 218D, rotational levers 216A and 216B, DOWN electrodes C11 220B and C11 220C, and UP electrodes C21 220A and C21 220D. In this embodiment as is seen there is only one anchor A 210B that connects the two central springs B1 214A and B2 214B.

Single Lever Design

FIG. 3 shows a single lever and single anchor accelerometer 300 in accordance with an embodiment.

The spring B 314B connects the anchor A 310B to the lever L 316B. The two external torsional springs B21 318B and B22 318D connect the end of the lever to the two proof masses PM1 302B and PM2 302A. The two proof masses are coupled to the substrate with two translating out-of-plane springs.

The two translating springs B11 318A and B12 318C must be stiff for rotation around X to have the two proof masses moving in anti-phase direction normal to the plane of the substrate. If those springs are compliant for rotation around the X axis then the sensor 300 rotates around X axis.

A linear acceleration cause a force on each of the two proof masses PM1 302A ad PM2 302B that is transferred to the lever L 316B and provides a torque on the central spring B 314B. Moreover, if there is an unbalancing in the mass and lever product then the central spring B 314B and the lever L 316B rotate and one of the proof masses moves towards the substrate and the other of the proof masses PM1 302A and PM2 302B moves in the opposite direction.

Alternative Single Lever Accelerometer

FIG. 4 shows an alternative single lever accelerometer 400 in accordance with an embodiment. The single lever comprises proof masses 402A and 402B, anchor 410B, rotational lever 416B, translating springs B11 418A and B12 418C, torsional springs B21 418B, B 414B and B22 418D, DOWN electrodes C1 420A, and UP electrodes C2 420B. As explained in FIG. 3, the translating springs B11 418A and B12 418C must stiff for rotation around the X axis to have the two proof masses moving in anti-phase direction normal to the plane of the substrate.

Two MEMS Accelerometers

FIG. 5a shows the configuration of the sensor to be a capacitive wheatstone bridge in accordance with an embodiment. FIG. 5b shows a configuration for sensing acceleration in a Wheatstone bridge configuration as shown in accordance with an embodiment. FIG. 5c shows a configuration for sensing magnetic field in a Wheatstone bridge configuration as shown in accordance with an embodiment. FIG. 5a shows the configuration of the sensor to be a capacitive wheatstone bridge in accordance with an embodiment. The sensor 500 a comprises proof masses 502A and 502B, anchors 510A and 510B, torsional springs 514A, 514B, 518A, 518B, 518C and 518D, rotational levers 516A and 516B, UP electrodes C21 (FIGS. 5b and 5c ) 520A, C21 (FIGS. 5b and 5c ) 520D, C22 (FIGS. 5b and 5c ) 520A and C22 (FIGS. 5b and 5 c) 520D, and DOWN electrodes C11 (FIGS. 5b and 5c ) 520B, C11 (FIGS. 5b and 5c ) 520C, C12 (FIGS. 5b and 5c ) 520B and C12 (FIGS. 5b and 5c ) 520C. In response to acceleration the proof masses 502A and 502B moves in an anti-phase direction normal to the substrate increasing the capacitance of capacitors C11 and C12 and decreasing the capacitance of the capacitors C21 and C22. For sensing acceleration, the capacitors C11, C21, C12, and C22 can be connected in a Wheatstone bridge configuration as shown in FIGS. 5b and 5 c.

MEMS Accelerometer with Capacitive Readout on Rotational Lever

FIG. 6 shows an accelerometer 600 where a capacitive readout is performed on electrodes on levers instead on proof masses in accordance with an embodiment. The sensor comprises proof masses 602A and 602B, rotational levers 616A and 616B, anchors 610A and 610B, torsional springs 614A, 614B, 618A, 618B, 618C, 618D, UP electrodes C21 620A and C21 620D, and DOWN electrodes C11 620B and 620C. As is seen, the electrodes 620A-620D are utilized to detect movement of the rotational levers 616A and 616B.

MEMS Accelerometer with Tilt Cancellation Paddles

FIG. 7 shows an accelerometer 700 including the tilt cancellation paddles in accordance with an embodiment. The sensor comprises proof masses 702A and 702B, torsional springs 714A, 714B, 718A, 718B, 718C and 718D, rotational levers 716A and 716B, UP electrodes C21 720A and C21 720D, DOWN electrodes C11 720B and C11 720C, and tilt cancellation paddles 722A, 722B, 722C and 722D. The proof masses 702A and 702B move in anti-phase direction normal to the plane of the substrate with the tilt cancellation paddles 722A and 722B. The output induced by a tilt between proof masses and the substrate is canceled by measuring the differential capacitance between tilt cancellation electrodes and UP and DOWN electrodes.

Accelerometer and Magnetometer Sensor with Differential Capacitive Sensing

FIG. 8 shows a combined accelerometer and magnetometer sensor in accordance with an embodiment. The combined accelerometer and magnetometer sensor 800 comprises proof masses 802A and 802B, anchors 810A and 810B, torsional springs 814A, 814B, 818A, 818B, 818C and 818D, magnetic materials 816A and 816B, UP electrodes C21 820A and C22 820D, and DOWN electrodes C11 820C and C12 820B. The magnetic material induces a torque in response to a magnetic field. This torque will cause the sensor 800 to rotate around x axis. Moreover, acceleration causes the proof masses 802A and 802B to move in anti-phase direction normal to the plane of the substrate.

The acceleration and magnetic field can be sensed separately because they cause two different sensing modes, respectively the anti-phase movement of the proof masses and the tilting around the first axis. For instance the combined accelerometer and magnetometer sensor 800 measures by altering the configuration of a capacitive readout on a circuit shown in FIG. 5b and FIG. 5c . In particular the signals are given by: A _(out) ˜C ₁₁ +C ₁₂ −C ₂₂ −C ₂₁ M _(out) ˜C ₁₁ −C ₁₂ +C ₂₂ −C ₂₁ where A_(out) is the output given by the acceleration and M_(out) is the output given by the magnetic field.

Placement of Sensing Electrodes when Utilizing a Cap

A cap or a cover provides mechanical protection to a structural layer and optionally forms a portion of an enclosure for the sensor. When utilizing a cap on top of the substrate the sensing electrodes can be located in different areas on the sensor. To describe this feature in more detail refer now to the following discussion in conjunction with the accompanying Figures.

FIG. 9 illustrates a sensor 900 that includes a substrate 906 with a cap 950 coupled thereover with a sensor structure 901 coupled to the substrate by anchor 914 within a cavity 908 of the sensor. In this embodiment, the UP and DOWN electrodes 904A and 904B are coupled to the substrate 906.

FIG. 10 illustrates a sensor 900′ similar to that of FIG. 9 except that the UP and DOWN electrodes 904A and 904B are coupled to the cap. FIG. 11 illustrates a sensor 900″ that is also similar to that of FIG. 9 except that an UP electrode 904A and a DOWN electrode 904B are on the substrate and there is a DOWN electrode 904C and an UP electrode 904D on the cap 950. FIG. 12 illustrates a sensor 900′″ similar to FIG. 9 except that anchor 914 couples the sensor structure 901 to the cap 950 rather that the substrate 906. As is readily recognized by one of ordinary skill in the art, for example other embodiments could include on the sensor 900′″ electrodes 904 on both the cap 950 and the substrate 906 or any combination thereof or one up electrode on the cap and one electrode on the substrate or any combination thereof.

Accelerometer to Measure the Acceleration in Three Orthogonal Directions

FIGS. 13a-13c illustrate another embodiment of an accelerometer 1000 in accordance with the present invention. The accelerometer 1000 is similar to accelerometer 100 but further comprises in plane transducers Cx1 and Cx2 for measuring X motion of proof masses 102A and 102B and Cy1 and Cy2 for measuring Y motion of the proof masses 102A and 102B. Therefore 102A and 102B can be measured in the X, Y and Z direction. The in plane transducers can be differential capacitive sensing comprising electrodes Cx1 103A and 103B, Cx2 103C and 103D, Cy1 105C and 105D and Cy2 105A and 105B. The transducers 103A-D, are coupled to anchors 107A-D. The transducers 105A-D are coupled to anchors 109A-D. The differential output is then proportional to the motion of the proof masses 102A and 102B and the magnitude and direction of the acceleration can be sensed in any linear direction X, Y and Z.

In an embodiment, all the springs (114A-B and 118A-D) are compliant for rotation in-plane in addition to the torsional compliance out-of-plane. Therefore the springs (114A-B and 118A-D) allow the proof masses 102A and 102B to move out-of-plane caused by Z acceleration of sensor 1000 and also allow proof masses 102A and 102B to move in-plane caused by either X or Y acceleration of sensor 1000. In addition, springs B1 and B2 114A and 114B can also be compliant for translation in plane in the Y direction. Possible embodiments of such a spring are straight, curved or folded beam that is widely used in similar devices.

Since the springs (114A-B and 118A-D) are compliant for rotation the two lever arms L1 (116A) and L2 (116B) are in-plane rotational lever arms. If the springs rotate in-plane then the lever arms rotates in-plane. If the springs (114A-B and 118A-D) have torsional compliance then the lever arms L1 (116A) and L2 (116B) are torsional lever arms, meaning that they rotate out-of-plane. If the springs (114A-B and 118A-D) are translational, then also the lever arms L1 (116A) and L2 (116B) are translational and translate in-plane. The spring (114A-B and 118A-D) can be any combination of rotational, torsional and translational and therefore the levers L1 (116A) and L2 (116B) are also respectively rotational, torsional and translational.

X-direction acceleration of sensor 1000 results in an X direction force, F1 x, applied to a first proof mass 102A proportional to the weight of PM1 102A. The F1 x applied to proof mass 102A transfers to the springs B11 118A and B22 118D, the springs between PM1 102A and the levers 116A-B. In addition, acceleration of sensor 1000 further results in an X direction force, F2 x, applied to the second proof mass 102A, proportional to the weight of PM2 102B. F2 x applied to proof mass 102B transfers to springs B21 118B and B12 118C, the springs between PM2 102B and the levers 116A-B.

X-direction acceleration of sensor 1000 result in an unbalanced torque about lever arms 116A-B causing proof masses 102A-B to move in-plane. The unbalanced torque can be caused if PM1 102A has a different weight than PM2 102B or if lever L1 of 116A (between PM1 102B and the anchoring spring B11 114A or B12 114B) is different from lever L2 of 116B (between PM1 102B and the anchoring spring B21 114A or B22 114B). If the product of F1 x and L1 116A is different to the product of F2 x and L2 116B a net torque is applied to the lever causing PM1 102B and PM1 102A to translate in the x direction. The springs (114A-B and 118A-D) are designed to be compliant for in plane rotation. An in-plane unbalanced torque cause the springs (114A-B and 118A-D) and the levers (116A-B) to rotate in-plane, resulting in PM1 102A and PM2 102B to translate antiphase in the X direction, where PM2 102B moves in the same direction as the X direction acceleration and proof mass PM1 102A moves in the opposite direction as the X direction acceleration. This displacement caused by the in-plane acceleration of sensor 1000 is depicted in FIG. 13b , where the arrows indicate the displacement of PM1-2 102A-B. In FIG. 13b the unbalanced torque is caused by the difference in weight of PM1 102A and PM2 102B. The differential output on the electrodes is then proportional to the proof masses motion: Cx1−Cx2˜XPM2+XPM1.

FIG. 13c shows the displacement caused by Y direction acceleration of sensor 1000, where the arrows indicate the displacement of PM1-2 102A-B. Y direction acceleration of sensor 1000 applies a Y direction force (F1 y) to PM1 102B and a Y direction force (F2 y) to PM2 102A. The Force Fy1 and Fy2 cause PM1-2 102A-B to translate in the Y direction as the springs (114A-B and 118A-D) are compliant in the Y direction. The differential output on the electrodes (differential output=Cy1−Cy2=(105A+AO5B)−(105C+105D) is then proportional to the Proof Masses motion: Cy1−Cy2˜YPM2+YPM1.

In an alternative embodiment, the sensor can detect acceleration in X and Z only as shown in FIG. 13b with the transducers Cz and Cx only, or can detect acceleration in Y and Z only as shown in FIG. 13c with the transducers Cz and Cy only, or can detect acceleration in X and Y only with the transducers Cx and Cy only. In another embodiment sensor 1000 further comprises magnetic material disposed on PM1 102A and/or PM2 102B. In this embodiment the magnetic material is magnetized in-plane along a first axis. Wherein an in-plane magnetic field applied to sensor 1000 along a second axis, that is perpendicular to the first axis, causes an in-plane torque to be applied to the respective proof mass. The in-plane torque causes the respective proof mass to rotate in-plane and the motion can be detected with the in-plane electrodes. Wherein magnetic field applied to sensor 1000 out-of-plane along a third axis, that is perpendicular to the first axis, causes an out-of-plane torque to be applied to the respective proof mass. The out-of-plane torque causes the respective proof mass to rotate out-of-plane and the motion can be detected with the out-of-plane electrodes.

Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiments and those variations would be within the spirit and scope of the present invention. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the present invention. 

What is claimed is:
 1. A sensor comprising: a substrate; and a mechanical structure, wherein the mechanical structure includes: at least two proof masses including a first proof mass and a second proof mass; a flexible coupling between the at least two proof masses and the substrate; and a transducer for measuring motion in a direction normal and parallel to a plane of the substrate of the mechanical structure relative to the substrate, wherein the at least two proof masses move in an anti-phase direction normal to the plane of the substrate in response to acceleration of the sensor normal to the plane and move in anti-phase in a direction parallel to the plane of the substrate in response to an acceleration of the sensor parallel to the plane, and wherein the transducer is a capacitive sensor.
 2. The sensor of claim 1, wherein the first proof mass and the second proof mass have unbalancing torque.
 3. The sensor of claim 1, wherein the flexible coupling further comprises: at least one anchor; and a rotational and torsional system, wherein the rotational and torsional system further includes an anchoring spring connecting the at least one anchor, a first rotational lever and a second rotational lever, wherein a first rotational and torsional spring connects the first proof mass to the first rotational lever with a first lever length, and wherein a second rotational and torsional spring connects the second proof mass to the second rotational lever with a second lever length.
 4. The sensor of claim 3, wherein the first lever length and the second lever length are different.
 5. The sensor of claim 4, wherein the flexible coupling further includes: a second anchoring rotational and torsional spring connecting the at least one anchor and a second rotational and torsional lever; a third rotational and torsional spring connects the first proof mass to the second rotational lever with a third lever length; and a fourth rotational and torsional spring connects the second proof mass to the second rotational lever with a fourth lever length, wherein the first rotational lever and the second rotational lever rotate antiphase in a direction normal to the substrate in response to acceleration of the sensor normal to the substrate, and wherein the first rotational lever and the second rotational lever rotate antiphase in a plane parallel to the substrate in response to acceleration of the sensor parallel to the substrate.
 6. The sensor of claim 5, wherein the third lever length and the fourth lever length are different.
 7. The sensor of claim 1, further comprising a magnetic material, wherein the magnetic material is on any of the at least two proof masses, the first rotational lever, and the second rotational lever, and wherein the mechanical structure rotates in another plane parallel to the plane in response to the magnetic field in a direction parallel to the plane.
 8. The sensor of claim 1, further comprising a magnetic material, wherein the magnetic material is on any of the at least two proof masses, the first rotational lever, and the second rotational lever, and wherein the mechanical structure rotates in a directional normal to the plane in response to the magnetic field in a direction normal to the plane.
 9. The sensor of claim 1, further comprising a magnetic material, wherein the magnetic material is on any of the at least two proof masses, the first rotational lever, and the second rotational lever.
 10. The sensor of claim 1, wherein the mechanical structure rotates in a directional normal to the plane in response to a magnetic field in a direction normal to the plane.
 11. A sensor comprising: a substrate; and a mechanical structure, wherein the mechanical structure includes: at least two proof masses including a first proof mass and a second proof mass, a flexible coupling between the at least two proof masses and the substrate; and a transducer for measuring motion in a direction normal and parallel to a plane of the substrate of the mechanical structure relative to the substrate, wherein the at least two proof masses move in an anti-phase direction normal to the plane of the substrate in response to acceleration of the sensor normal to the plane and move in anti-phase in a direction parallel to the plane of the substrate in response to an acceleration of the sensor parallel to the plane, wherein the at least two proof masses move in a direction parallel to the plane of the substrate in response to an acceleration of the sensor parallel to the plane, and wherein the transducer is a capacitive sensor.
 12. The sensor of claim 11, wherein the first proof mass and the second proof mass have unbalancing torque.
 13. The sensor of claim 11, wherein the flexible coupling further comprises: at least one anchor; and a rotational, translational and torsional system, wherein the rotational, translational and torsional system further including an anchoring spring connecting the at least one anchor, a first rotational lever and a second rotational lever, wherein a first rotational, translational and torsional spring connects the first proof mass to the first rotational torsional lever with a first lever length, and wherein a second rotational, translational and torsional spring connects the second proof mass to the second rotational lever with a second lever length.
 14. The sensor of claim 13, wherein the first lever length and the second lever length are different.
 15. The sensor of claim 14, wherein the flexible coupling further includes: a second anchoring rotational, translational and torsional spring connecting the at least one anchor and a second rotational, translational and torsional lever; a third rotational, translational and torsional spring connects the first proof mass to the second rotational, translational and torsional lever with a third lever length; and a fourth rotational, translational and torsional spring connects the second proof mass to the second rotational, translational and torsional lever with a fourth lever length.
 16. The sensor of claim 15, wherein the third lever length and the fourth lever length are different.
 17. The sensor of claim 15, further comprising magnetic material, wherein the magnetic material is on any of the at least two proof masses, the first rotational lever, and the second rotational lever.
 18. The sensor of claim 11, further comprising a magnetic material, wherein the magnetic material is on any of the at least two proof masses, the first rotational lever, and the second rotational lever, and wherein the mechanical structure rotates in another plane parallel to the plane in response to the magnetic field in a direction parallel to the plane.
 19. The sensor of claim 11, further comprising a magnetic material, wherein the magnetic material is on any of the at least two proof masses, the first rotational lever, and the second rotational lever, and wherein the mechanical structure rotates in a directional normal to the plane in response to the magnetic field in a direction normal to the plane.
 20. The sensor of claim 11, wherein the transducer is on any of the two proof masses, or the mechanical structure, or lever arms associated with the two proof masses.
 21. The sensor of claim 11, wherein the transducer is a capacitive sensor. 